The present invention relates to a novel glycol ether dry-cleaning solvent and a method for effecting dry-cleaning using said solvent. More particularly, the present invention relates to a glycol ether solvent that not only is comparable or superior to perchloroethylene in its attributes and benefits, and does not suffer from the serious environmental, health and occupational negatives and problems associated with the use of perchloroethylene, but which also represents an improvement over the current glycol ether solvents that are contemplated as replacements for perchloroethylene.
Perchloroethylene is the most widely used dry-cleaning solvent, and is commonly referred to (and will be referred to sometimes hereinafter) as "perc". Perc is a chlorinated hydrocarbon-based solvent. It is the dry-cleaning solvent of choice throughout North America, Europe and Asia.
In addition to perc's use in the dry-cleaning industry, it has found extensive use as a degreasing agent in the metals industry, in the scouring/milling of wool, and in various "clean room" applications in the semiconductor and electronics industries. The industrial uses of perc are approximately ten-fold greater than its use as a solvent for dry cleaning.
While perc has been found to be an effective dry-cleaning agent because it is non-flammable, does not damage synthetic fabrics or cause shrinkage to fabrics containing naturally occurring fibers, such as wool, and has a relatively low boiling point that permits its being reclaimed and purified by means of ordinary distillation, it does present a number of other problems which present drawbacks to its use. In particular, perchloroethylene presents a number of health and environmental hazards that would militate against its continued use, provided a substitute solvent of comparable quality were available that was free of the aforementioned hazards.
Because perc is heavier than water, its disposal represents a significant environmental risk because it will sink to the bottom of an aquifer, lake, river, and the like, with possibly resultant contamination of the water supply. Additionally, perc vapors have been implicated as having a deleterious effect on the central nervous system. In addition, because it is a highly chlorinated molecule, perc has been identified as being a significant health hazard to cattle, and as a cause of skin cancer, particularly melanoma, because of the action of the chlorine in perc depleting oxygen from the ozone layer. Furthermore, and of particular import, is the fact that perc is not biodegradable and, hence, will over a period of time accumulate, presenting a significant industrial waste disposal hazard.
As the nature and seriousness of the foregoing problems become more and more manifest with the passage of time and with the completion of various research and clinical investigations into the nature of perc and its mechanisms of action, the use of alternative solvents has been sought, but none have met with any degree of commercial success since they could not match the result obtained by perc as a dry-cleaning agent.
However, at this point in time, when environmental concerns are being rigorously monitored and policed by domestic and foreign governments by means of legislation and civil and even criminal prosecution, the need for a substitute solvent for perc for dry-cleaning operations, as well as other operations, has become a matter of some degree of urgency.
A difficulty in identifying a replacement dry-cleaning solvent for perc is that it must meet so many requirements, both as to its efficacy as a dry-cleaning agent, i.e. high purity, non-shrinking with respect to about 160 types of fabric, dye-fast for non-bleeding with respect to about 900 types of dyes, a high flashpoint to render it non-flammable and non-combustible, the ability to separate from water, effective detergency, ease of distillation, simplicity of reclamation, compatibility with existing dry-cleaning equipment, and the like, as well as its being non-polluting to the water supply and the ozone layer, biodegradable, non-toxic, non-carcinogenic, and the like.
One proposed solvent substitute, namely propylene glycol monomethyl ether, which is disclosed in EP 479,146 as possessing many desirable properties, was found to be wanting in that it causes damage to weak dyes, fine yarns, and delicate fabrics, such as acetates, because of its pronounced tendency to accumulate water from the environment, and from fabrics being dry-cleaned. Water accumulation or water-miscibility is also a decided negative from another aspect in that it significantly impairs the efficiency of the dry-cleaning process because the dry-cleaning equipment is burdened with the handling of excessive quantities of water and the solvent stock is diluted and must be brought back to a correct ratio for stability reasons.
Propylene glycol tertiary-butyl ether (PTB) and propylene glycol n-butyl ether (PNB) were disclosed by WO 98/45523 as being superior alternatives to propylene glycol monomethyl ether. PTB and PNB were disclosed to possess all of the dry-cleaning attributes associated with perc and none of its drawbacks. The water-absorbing capabilities of both solvents was disclosed to be within a range effective in preventing damage to acetates and the tendency of woolen garments to shrink in water. The water absorption also lowered the solvent boiling point while raising the flashpoint. Both solvents were also disclosed to be non-pollutants of the water supply and ozone layer, biodegradable, non-toxic and non-carcinogenic. In addition, both solvents were capable of being used in existing perc dry-cleaning equipment.
Aqueous PTB and PNB dry-cleaning compositions have flashpoints within industry standards. However, there has recently been a regulatory trend toward a higher flashpoint standard. Furthermore, regulatory agencies are also considering making the standard applicable to individual components of a composition, even if the flashpoint of the overall composition meets industry standards. Accordingly, there exists a need for dry-cleaning compositions based on higher flashpoint glycol ethers.
The conventional wisdom has been, however, that higher flashpoint glycol ethers make poor dry cleaning solvents because they are too incompatible with water. While glycol ether dry-cleaning solutions containing too much water are undesirable because of the consequential shrinkage to woolens and damage to acetates, not to mention the solvent dilution, a low water content hampers the ability of the dry cleaning composition to remove water-soluble stains, which make up the bulk of stains to be removed from garments requiring dry cleaning. Thus, the need for dry-cleaning compositions based on higher flashpoint glycol ethers remains unsatisfied.